The present invention relates to a method for improving surface properties of a shaped article made of a thermoplastic or thermosetting synthetic resin such as a vinyl chloride-based resin or, more particularly, to a method for reducing electrostatic charging or accumulation of static electricity on the surface of a shaped article of a synthetic resin.
As is well known, shaped articles of a synthetic resin in general or, in particular, a vinyl chloride-based resin (hereinafter referred to as PVC resin) are remarkably susceptible to the accumulation of static electricity on the surface thereof bringing about several problems of not only dirtiness of the appearance caused by the deposition or clogging of dusts on the surface but also the unpleasant influence to the human body in contact therewith by the electric shock with the static electricity accumulated on the surface and the danger of spark discharge.
Various attempts have been made to find an effective way or method for overcoming the above mentioned disadvantages of shaped articles of a synthetic resin by the improvement of the surface properties leading to the decrease of the electrostatic charge on the surface.
For example, such an anti-static effect is obtained by coating the surface of the article with a surface active agent known to be effective as an anti-static agent. This method is advantageous when the anti-static effect is to be exhibited instantly but is defective in the relatively poor durability of the effect as well as in the sticky touch of the coated surface which eventually leads to blocking of the shaped articles with each other.
Another way to reduce the electrostatic charge on the surface of a shaped article of a synthetic resin is to admix the resin with an anti-static agent, e.g. surface active agent, before the resin is shaped into the shaped article by molding. This method is satisfactory in the durability of the anti-static effect but the effectiveness of the method is impractically low when the amount of the anti-static agent is limited. When the amount of the antistatic agent incorporated into the resin is increased to such an extent that a practically significant anti-static effect is obtained, there may also be caused problems of sticky touch on the surface leading to blocking and readiness to stain in addition to coloring of the surface as well as the detrimental effect on the heat resistance of the shaped article if not to mention the adverse effect on the workability of the resin per se admixed with the anti-static agent in such a large amount.
On the other hand, there has been recently proposed a method in which the surface of a shaped article of a synthetic resin can be rendered more hydrophilic when the surface is subjected to exposure to a low temperature plasma of certain kinds of inorganic or organic gases whereby the accumulation of static electricity on the surface can be reduced to some extent. This method is, however, not satisfactory due to the relatively low effectiveness and the poor durability of the effect not to warrant the practical application of the method.